Weather resistant ungrounded power line sensor

ABSTRACT

An ungrounded power line sensor system includes a housing configured for coupling about a power line, at least a first voltage sensing plate supported by the housing and exposed to rain and snow, and at least a second voltage sensing plate supported by the housing and shielded from rain and snow. Voltages sensed by the first and second voltage sensing plate are separately measured in order to mitigate variations in the two measurements due to a weather event, for example by applying a weighted average calculation to the measurements to cancel out the effects of rain on the first voltage sensing plate.

FIELD OF THE INVENTION

This invention relates to power line sensors and methods.

BACKGROUND OF THE INVENTION

Ungrounded power line sensors measure the voltage of a medium-voltagepower line relative to ground through, for example, a capacitivecoupling between metal plates on the outside of the sensor and ground.See U.S. Pat. No. 4,689,752 incorporated herein by this reference. Undernormal conditions, accurate voltage measurements are possible. However,the accumulation of rain, snow, and/or ice on the sensor can change thecapacitive coupling between the sensor and ground resulting in errors inthe measurement of line voltage.

U.S. Pat. No. 4,795,973 (incorporated herein by this reference)describes a modification to a sensor with the objective of being lesssensitive to snow. The entire sensor body is turned into a single, largevoltage sensing plate. Such an approach may still be somewhat sensitiveto snow because significant snow build-up will change the effectivesurface area of the sensor.

To be completely resistant to the effects of snow and ice, one typicalsolution is to use relatively large and heavy instrumentationtransformers wired directly to each phase. A “Potential Transformer”(PT) is used to transform the line voltage down to a lower voltage thatis more easily measured, typically about 120 Vrms. By measuring thislower voltage and multiplying by the turns ratio of the PT, theline-to-neutral voltage of a phase can be deduced. A “CurrentTransformer” (CT) is used to measure current. The line to be monitoredpasses once through a transformer core. A secondary with many turns isalso wound around the transformer core, and the secondary is eithershorted or drives a very small resistance. The secondary is isolatedfrom the voltage on the primary, and the current on the secondary ismuch lower than (and proportional to) the current on the line, with theturns ratio of the transformer again being the proportionality constant.Voltage, current, power, etc., are then measured by a commercial meterattached to the PT and CT (for example, the ITRON Quantum Q1000).

Such a solution, however, can be expensive and labor intensive toinstall.

SUMMARY OF THE INVENTION

An ungrounded power line sensor measures the voltage of a medium-voltagepower line relative to ground through a capacitive coupling betweenelectrically conductive plates on the outside of the sensor and ground.Under normal conditions, accurate voltage measurements are possible.However, the presence of raindrops sitting on the surface of the sensorcan change the capacitive coupling between the sensor and groundresulting in measurement errors in the line voltage. If two sets ofvoltage sensing plates are employed, one on top of the sensor and one onthe bottom of the sensor, we discovered that the top plates tend toexhibit an increase in voltage in the presence of rain whereas thebottom plates tend to experience a decrease in voltage in the rain. Byseparately measuring the top and bottom plates, the presence of rain canbe detected by the difference in the readings of the top and bottomplates. The deviation in sensor readings due to the rain can also bemitigated by computing a weighted average of the top and bottom sensorplate readings to yield a combined voltage reading that is insensitiveto rain.

Featured is an ungrounded power line sensor system comprising a housingconfigured for coupling about a power line, at least a first voltagesensing plate supported by the housing and exposed to rain and snow, andat least a second voltage sensing plate supported by the housing andshielded from rain and snow. A processing subsystem is configured to(e.g., runs computer instructions which) measure a voltage sensed by thefirst voltage sensing plate, separately measure a voltage sensed by thesecond voltage sensing plate, and mitigate variations in saidmeasurements due to a weather event by, for example, applying a weightedaverage calculation to the voltage measurements to cancel out theeffects of rain on the first voltage sensing plate.

In one example, the measured voltage sensed by the first voltage sensingplate is V_(top), the measured voltage sensed by the second voltagesensing plate is V_(bottom), and the weighted average calculation isV_(avg)=(1−c)V_(top)+c V_(bot) where c is a constant weighting factor.

The system may further include a current sensor and then the processingsubsystem preferably measures power and energy using a currentmeasurement output by the current sensor and a measured voltage sensedonly by the second voltage sensing plate. The purpose of computing powerand energy using only the bottom plate is that it has been observed thatvoltage measurements from the top plates can be erroneously shifted inphase during snow conditions, whereas the bottom plates (which do notaccumulate snow) have little or no phase shift due to snow. In someembodiments, the processing subsystem is configured to apply a scalingfactor to the power and energy measurements. The scaling factor may be afunction of the measured voltage sensed by the first voltage sensingplate and the measured voltage sensed by the second voltage sensingplate. In one example, the measured voltage sensed by the first voltagesensing plate is V_(top), the measured voltage sensing by the secondvoltage sensing plate is V_(bot), and the scaling factor is(1−c)V_(top)+c V_(bot) divided by V_(bot) where c is a constantweighting factor.

The processing subsystem may also mitigate variations in the voltagemeasurements by comparing the measured voltage sensed by the firstvoltage sensing plate and the measured voltage sensed by the secondvoltage sensing plate. The processing subsystem can be configured toreport a snow event when the measured voltage sensed by the firstvoltage sensing plate differs from the measured voltage sensed by thesecond voltage sensing plate by a predetermined value.

In one version there is a set of electrically connected voltage sensingplates exposed to rain and snow and a set of electrically connectedvoltage sensing plates shielded from rain and snow. The system housingmay have an apex between opposing outwardly sloping top voltage sensingplates exposed to rain and snow and opposing inwardly sloping bottomvoltage sensing plates shielded from rain and snow. In some embodiments,the processing subsystem includes a first processor in the housingelectrically connected to the first voltage sensing plate and separatelyelectrically connected to the second voltage sensing plate. The systemcollector may also include a second processor in the collector. Thus,the processing subsystem can reside in the sensor, the collector, or canbe distributed between those two components.

Also featured is an ungrounded power line sensing method comprisingmeasuring a voltage sensed by a first voltage sensing plate locatedproximate a power line and exposed to rain and snow, separatelymeasuring the voltage sensed by a second voltage sensing plate locatedproximate a power line but shielded from rain and snow, and mitigatingvariations in the voltage measurements due to a weather event.

In one embodiment, an ungrounded power line sensor system includes ahousing configured for disposal about a power line, a current sensorassociated with the housing for measuring power line current, a firstvoltage sensing plate supported by the housing and exposed to rain andsnow, and a second voltage sensing plate supported by the housing andshielded from rain and snow. A processing subsystem is configured tomeasure a voltage sensed by the first voltage sensing plate, measure avoltage sensed by the second voltage sensing plate, mitigate variationsin said measurements by applying a weighted average calculation to thevoltage measurements to cancel out the effects of rain on the firstvoltage sensing plate, and measure power and energy using the power linecurrent measurement and only the measured voltage sensed by the secondvoltage sensing plate.

An ungrounded power line sensing method includes measuring a voltagesensed by a first voltage sensing plate proximate a power line andexposed to rain and snow, measuring a voltage sensed by a second voltagesensing plate proximate a power line and shielded from rain and snow,measuring power line current, applying a weighted average calculation tosaid voltage measurements to cancel out the effects of rain on the firstvoltage sensing plate, and measuring power and energy using the measuredcurrent and only the measured voltage sensed by the second voltagesensing plate.

The subject invention, however, in other embodiments, need not achieveall these objectives and the claims hereof should not be limited tostructures or methods capable of achieving these objectives.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 is a schematic view showing three sensors deployed on a powerline in accordance with an example of the invention;

FIG. 2 is a schematic three dimensional view of a prior art sensor;

FIG. 3 is a graph showing voltage versus time and how the prior artsensor of FIG. 2 voltage output varies from the true power line voltageduring a rain event;

FIG. 4 is a schematic three dimensional view showing a new sensor inaccordance with an example of the subject invention;

FIG. 5 is a schematic cross sectional view of the sensor shown in FIG.4;

FIG. 6 is a block diagram showing the primary components associated withthe sensor of FIGS. 4-6;

FIG. 7 is a block diagram showing the primary components associated witha sensor subsystem wirelessly communicating with a collector powered bya single phase transformer in accordance with aspects of the invention;

FIG. 8 is a block diagram showing the primary components associated withthe collector of FIG. 7;

FIG. 9 is a graph showing the voltage measured by the sensor subsystemof the subject invention compared to the actual voltage and the voltagemeasured by a prior art sensor during a rain event; and

FIG. 10 is a graph showing the power error over time reported by asensor processing subsystem configured in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, thisinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Thus, it is to be understood that theinvention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. If only oneembodiment is described herein, the claims hereof are not to be limitedto that embodiment. Moreover, the claims hereof are not to be readrestrictively unless there is clear and convincing evidence manifestinga certain exclusion, restriction, or disclaimer.

In FIG. 1, three sensors 10 a, 10 b, and 10 c are mounted on a mediumvoltage three-phase power distribution feeder, one sensor on each phaseof the feeder. Under normal conditions, sensors 10 a, 10 b, and 10 c canmeasure voltage accurately to +/−0.5% so long as the sensor iscalibrated in place after installation. The sensors communicate viaradio to a collector 12 located on a nearby utility pole. A single-phasetransformer 35 is attached between Phase “B” of the feeder and theneutral line. The transformer supplies the 120V power needed to powercollector 12. See U.S. application Ser. No. 14/061,128 incorporatedherein by this reference.

Shown in FIG. 2 is a prior art sensor 10 with housing 18 configured fordisposal about power line 20. The housing supports voltage sensing plate16 a shielded from rain and snow. FIG. 3 shows the output of the phaseA, phase B, and phase C sensors of the FIG. 2 design compared to areference measuring the actual voltage in each phase. As shown in FIG.3, the prior art sensor voltage measurements are fairly inaccurate inrain.

Shown in FIG. 4 is a new sensor 10′ with housing 18 configured fordisposal about power line 20. The housing supports first voltage sensingplate 14 a exposed to rain and snow and second voltage sensing plate 16a shielded from rain and snow. In this particular example, housing 18 isa polyhedron with apex 22, FIG. 5, downwardly and outwardly slopingopposing sides 13 a and 13 b supporting a set of top voltage sensingplates 14 a and 14 b and downwardly and inwardly sloping sides 15 a and15 b supporting a set of bottom voltage sensing plates 16 a and 16 b.The two top plates 14 a and 14 b may be electrically interconnected andthe two bottom plates 16 a and 16 b may be electrically interconnected.In other versions, there is only one top plate and one bottom plate.And, other housing configurations are possible.

One discovery by the inventors hereof is that during a rain event thevoltage measured by the top voltage sensing plate set (14 a, 14 b)increases and the voltage measured by the bottom sensing plate setdecreases, even though the actual voltage of the line is unchanged. Thetop voltage sensing plate set (14 a, 14 b) experiences an increase incapacitance between the sensor plates and ground due to the raindroplets adding surface area to the top voltage sensing plate set (16 a,16 b). This increase in capacitance causes the voltage measured by thetop plates to increase. Even though there is no direct contact of rainwith the lower voltage plates, the increased surface area of the topvoltage plates and top sensor body due to rain causes charges to bepreferentially distributed on the upper part of the sensor, ultimatelyreducing the voltage measured by the bottom voltage sensing plate set.

In the subject invention, microcontroller 30, FIG. 6 is separatelyconnected electrically to the top voltage sensing plate 14 and thebottom voltage sensing plate 16 via conditioning circuitry as shown at32 a and 32 b.

There is capacitive impedance between the sensor plates and ground,represented in FIG. 6 by capacitances Ctop and Cbot. The value of eachcapacitance is typically on the order of 1 picofarad. Controller 30 isused to measure the very small current that flows back and forth fromthe power line to the surface of each set of plates due to thesecapacitances. These currents are measures of the voltage between thepower line and ground.

Internal to the sensor, separate sensing circuits are used to conditionvoltage measurements from the top and bottom plates as shown in FIG. 6.Both top and bottom plate channels are sampled synchronously bymicrocontroller 30.

On sensor install, the relationship between the voltage measured by thesensor circuit and the line-to-neutral voltage must be calibrated. Thesensor system automatically and separately calibrates the readings fromthe top and bottom voltage sensor plates 14, 16.

Internal to the microcontroller, the RMS voltage of the top plate 14 iscalculated (denoted V_(top)). The RMS voltage of the bottom plate 16 isalso calculated (V_(bottom)) along with real and reactive power andenergy which are a combination of voltage and current measurements. Thepower and energy quantities are preferably calculated only using thebottom voltage sensor plate 16 for the voltage input to themicrocontroller because the bottom sensor plate, shielded by the sensorbody, experiences little or no phase shift in snow conditions.

Microcontroller 30 is thus configured to measure the voltage V_(top)sensed by the top voltage sensing plate(s) 14 and to separately measurethe voltage V_(bottom) sensed by the bottom voltage sensing plate(s) 16and to mitigate variations between V_(top) and V_(bottom).

Preferably, when V_(top) differs from V_(bottom) by a predeterminedamount (e.g., a −1% to +4% difference between top and bottom platevoltages), microcontroller 30 outputs a signal transmitted wirelessly bysensor transmitter 36 to radio 64 of collector 33, FIGS. 7-8. Collectorprocessor 62 (or microcontroller 44) is then configured to process thissignal and log a rain event or, alternatively, to correct and adjust thevoltage measurements as discussed below. In some examples, theprocessing subsystem functionality described herein is carried out bythe microcontroller 30, FIG. 6 of the sensor and/or the microcontrolleror microprocessor (44, 62, FIG. 8) of the collector. Various processinghardware may be used including applications specific integratedcircuits, field programmable gate arrays, and the like programmed tocarry out stored or uploaded computer instructions as explained herein.

The sensor 10′, FIG. 6 may further include a current sensor 31 such as aRogowski coil disposed about the power line 20 providing an output tomicrocontroller 30 for measuring the current of the power line 20 andtransmitting the current measurement via transmitter 36 to the radio 64of collector 33, FIGS. 7-8.

Collector 33 is preferably powered from transformer 35, FIG. 7preferably connected to ground 19 and one phase 18 a of the feeder beingmonitored by a feeder meter sensor 10 a. The single-phase transformer 18a used to power collector 12 reduces the medium voltage of thedistribution line to a tractable voltage near 120 Vrms. The supplyvoltage to collector 12 is related to the feeder 18 a voltage by thetransformer 14 ratio of the transformer supplying the collector.

The collector supply voltage 37 is fed into a voltage conditioningcircuit 42. This circuit preferably including a voltage divider and anop amp buffer reduces the voltage from the 120V supply voltage to a lowvoltage in the range of a few volts for measurement with anAnalog-to-Digital Converter (ADC). In the initial reduction to practice,a circuit based on the LTC 1992 differential Op Amp was employed. Thesignal output by the circuit 42 is then repeatedly measured by an ADCbuilt into microcontroller chip 44 of the collector. In the oneprototype device, a TI MSP-430 class microcontroller samples anassociated 16-bit ADC at a rate of 2048 Hz. A True RMS-type filter (inthe prototype implementation, taking the RMS by squaring the sensedsignal, applying a low-pass, and taking the square-root of the result)is then applied in software operated on the microcontroller 44.

The microcontroller 44 also communicates with the sensors via a 2.4 GHzIndustrial, Scientific, and Medical (ISM) band radio module 64 obtainingmeasurements of voltage, current, power, and energy from the sensors.The microcontroller 44 passes both sensor and the collector supplyvoltage measurement to microprocessor 62 running embedded Linux.Software on the microprocessor 62 applies scaling factors determinedduring calibration to the phase voltage measurement from the sensors.Collector calibration factors, also determined during calibration, maybe applied to the collector supply voltage measurement to produce analternative voltage for each phase. The software may then compares thealternative and phase voltages to determine if there is a snow conditionand logs and/or corrects various measurements for the snow condition.The microprocessor 62 may use a Secure Digital (SD) Memory Card 72 tolocally store the collected data may use an Ethernet module 66, a 900MHz mesh radio 68, or a WiFi Radio 70 to transmit the collected data toend consumers of the data (e.g. SCADA systems). The voltage measurementcircuit configured to measure the collector's supply voltage, however,could be implemented in other ways. Only one preferred embodimentincludes voltage conditioning circuit 42, microcontroller 44, andmicroprocessor 62. See U.S. patent application Ser. No. 14/621,696incorporated herein by this reference.

In addition to simply detecting the presence of rain, the sensor systemcan correct for the presence of rain. Once per minute, a snapshot of allof a sensor's registers (i.e. voltages, current, power, energy, etc.) istaken and sent to the collector. At that time, the deviation in sensorreadings due to the rain can also be mitigated by computing andreporting a weighted average of the top and bottom voltage sensorplate(s) readings to yield a combined voltage reading that isinsensitive to rain. The weighted average is thus:

Vavg=(1−c)Vtop+cVbot;   (1)

where c is a constant weighting factor that is selected based onexperimental measurement of the sensor's performance in the rain.Collector 33 radio 70 transmits this computation to end users.

Power and energy values, which are computed using exclusively voltagemeasurements from the bottom plate, can then be adjusted by multiplyingby a scaling factor.

For example, the measured real power is the instantaneous voltagemultiplied by the instantaneous current. Here, the instantaneous voltageis the voltage measured only by bottom sensor plate 16, FIG. 5 and theinstantaneous current is the current measured by current sensor 31.Then, the processing subsystem is configured to report a real powervalue which is the measured real power multiplied by a scaling factorwhich may be

V_(avg)/V_(bot).   (2)

Measured reactive power, incremental volt-hours, incremental realenergy, and incremental reactive energy and the like are similarlyadjusted by the same scaling factor.

Since the power and energy measurements were computed using exclusivelythe bottom plate, the power factor and therefore the power and energycomputations will be accurate in snow conditions where snow effects arecorrected as described in U.S. patent application Ser. No. 14/621,696incorporated herein by this reference. The adjustment by the weightedaverage voltage yields robustness to the influence of rain as well.

Note that the computation of V_(avg) and the associated scalingoperation could be performed either in the sensor prior to sendingmeasurements to the collector or the computation could be performed inthe collector itself. In the presently implemented version, thecomputation of V_(avg) and the adjustment of power and energy valuestakes place in the sensor.

Also note that the scaling factor could be computed using either theinstantaneous top and bottom voltages at the time at which a snapshot istaken or by using the average voltage over the entire, nominallyone-minute, reporting period. Initial implementations used theinstantaneous voltages to perform the adjustment. Later implementationsuse the average top and bottom voltage over the reporting period toprovide greater robustness to special situations e.g. where the rainbegins part way through the reporting period.

Although a simple linear combination of V_(top) and V_(bot) was used inthe initial implementation, other more elaborate combinations of V_(top)and V_(bot) might be used in the future, on the basis of future fieldtesting and experimental results. For example, some nonlinear blend ofthe two voltages may yield improved performance. Alternately, thecombination of plates could be the result of a real time adaptive anddynamic ratio that results from analysis of top and bottom platevoltages and predictive modeling, i.e. incorporating information fromprevious values of V_(top) and V_(bot) to yield more accurate adjustedvalues.

In practice, the weighted average scheme provides acceptable rainaccuracy. For example, a pilot test site in Mission, BC measured thevoltages as pictured in FIG. 9 at a site at which both older two-plateand newer four-plate/two-channel sensors were monitoring the same mediumvoltage line. As shown in FIG. 10, the power error is also acceptable.

The separate sensing of top and bottom sensors allows partial mitigationof snow effects in instances where other adjustments are not applicable(i.e. when there is no direct access to supply voltage or in cases wherethe supply voltage has no correlation to the voltage of the mediumvoltage line). When snow conditions occur, the difference in voltagebetween the top and bottom plates exceeds the difference that isnormally expected during rainy conditions.

If the discrepancy between top and bottom plates is large enough toindicate snow conditions, the sensors can then communicate thiscondition to external equipment that is monitoring the sensor'smeasurements. For example, the sensors might communicate thisinformation digitally, e.g. via a field in the sensor's DNP3 messaginginterface. A more elaborate implementation of snow reporting couldincorporate the temperature reading of the sensor and use additionallogic to infer actionable weather information which would then betransmitted back to the utility, e.g. indicating the presence ofpotentially damaging freezing rain conditions versus more benignsnowfall, etc.

An indication of a snow condition can also be conveyed in an analogform. For one of implementations, the sensor is used as a voltage inputto a capacitor bank controller. The collector communicates with thecapacitor bank controller by producing an AC analog output voltageproportional to the voltage measured by the line-mounted sensor. Thecapacitor bank controller then measures the analog signal from thecollector as an indication of the line voltage (i.e. as if the sensorwere an electronic voltage transformer). If snow conditions are detectedby the system, the collector generates a low voltage, specificallychosen to be below the capacitor bank controller's “inhibit voltage”,the voltage below which capacitor switching functionality is disabled bythe capacitor bank controller. In this way, the capacitor bankcontroller will not switch during a snow event.

The strategy for identifying and indicating snow conditions in thecapacitor bank sensor scenario can be outlined as follows:

-   -   1) The sensor measure RMS voltage for both top and bottom        sensing plates and sends them to the collector;    -   2) The sensor computes real and reactive power based on the top        voltage and current (real and reactive power are used to        determine in-phase and out-of-phase portions of the current).    -   3) The top and bottom plates are separately calibrated during        install;    -   4) The collector has adjustable upper and lower error limits for        top and bottom plates, nominally set at −1%/+4%;    -   5) During operation, enter Voltage Error Mode if set voltage        equal to the predefined Error Voltage if % Error is out of        bounds.    -   6) During Voltage Error Mode, collector outputs a low-amplitude        AC voltage of prescribed amplitude to the capacitor bank        controller instead of producing an AC voltage proportional to        the RMS voltage measured by the sensor.    -   7) Otherwise, operate normally.

Although specific features of the invention are shown in some drawingsand not in others, this is for convenience only as each feature may becombined with any or all of the other features in accordance with theinvention. The words “including”, “comprising”, “having”, and “with” asused herein are to be interpreted broadly and comprehensively and arenot limited to any physical interconnection. Moreover, any embodimentsdisclosed in the subject application are not to be taken as the onlypossible embodiments.

In addition, any amendment presented during the prosecution of thepatent application for this patent is not a disclaimer of any claimelement presented in the application as filed: those skilled in the artcannot reasonably be expected to draft a claim that would literallyencompass all possible equivalents, many equivalents will beunforeseeable at the time of the amendment and are beyond a fairinterpretation of what is to be surrendered (if anything), the rationaleunderlying the amendment may bear no more than a tangential relation tomany equivalents, and/or there are many other reasons the applicant cannot be expected to describe certain insubstantial substitutes for anyclaim element amended.

Other embodiments will occur to those skilled in the art and are withinthe following claims.

What is claimed is:
 1. An ungrounded power line sensor systemcomprising: a housing configured for coupling about a power line; atleast a first voltage sensing plate supported by the housing and exposedto rain and snow; at least a second voltage sensing plate supported bythe housing and shielded from rain and snow; and a processing subsystemconfigured to: measure a voltage sensed by the first voltage sensingplate, separately measure a voltage sensed by the second voltage sensingplate, and mitigate variations in said measurements due to a weatherevent.
 2. The system of claim 1 in which the processing subsystem isconfigured to mitigate variations in said measurements by applying aweighted average calculation to said measurements to cancel out theeffects of rain on the first voltage sensing plate.
 3. The system ofclaim 2 in which the measured voltage sensed by the first voltagesensing plate is V_(top), the measured voltage sensed by the secondvoltage sensing plate is V_(bottom), and the weighted averagecalculation is V_(avg)=(1−c)V_(top)+c V_(bot) where c is a constantweighting factor.
 4. The system of claim 1 further including a currentsensor and wherein the processing subsystem is further configured tomeasure power and energy using a current measurement output by thecurrent sensor and a measured voltage sensed only by the second voltagesensing plate.
 5. The system of claim 4 in which the processingsubsystem is configured to apply a scaling factor to said power andenergy measurements.
 6. The system of claim 5 in which said scalingfactor is a function of the measured voltage sensed by the first voltagesensing plate and the measured voltage sensed by the second voltagesensing plate.
 7. The system of claim 6 in which the measured voltagesensed by the first voltage sensing plate is V_(top), the measuredvoltage sensing by the second voltage sensing plate is V_(bot) and thescaling factor is (1−c)V_(top)+c V_(bot) divided by V_(bot) where c is aconstant weighting factor.
 8. The system of claim 1 in which theprocessing subsystem is configured to mitigate variations in saidmeasurements by comparing the measured voltage sensed by the firstvoltage sensing plate and the measured voltage sensed by the secondvoltage sensing plate.
 9. The system of claim 8 in which the processingsubsystem is further configured to report a snow event when the measuredvoltage sensed by the first voltage sensing plate differs from themeasured voltage sensed by the second voltage sensing plate by apredetermined value.
 10. The system of claim 1 in which there are twoelectrically connected voltage sensing plates exposed to rain and snowand two electrically connected voltage sensing plates shield from rainand snow.
 11. The system of claim 10 in which the housing has an apexbetween opposing outwardly sloping top voltage sensing plates exposed torain and snow and opposing inwardly sloping bottom voltage sensingplates shielded from rain and snow.
 12. The system of claim 1 in whichthe processing subsystem includes a first processor in the housingelectrically connected to the first voltage sensing plate and separatelyelectrically connected to the second voltage sensing plate.
 13. Thesystem of claim 12 further including a collector and the processingsubsystem further includes a second processor in the collector.
 14. Anungrounded power line sensing method comprising: measuring a voltagesensed by a first voltage sensing plate proximate a power line andexposed to rain and snow; separately measuring the voltage sensed by asecond voltage sensing plate proximate a power line and shielded fromrain and snow; and mitigating variations in said measurements due to aweather event.
 15. The method of claim 14 in which mitigating variationsin said measurements includes applying a weighted average calculation tosaid measurements to cancel out effects of rain on the first voltagesensing plate.
 16. The method of claim 15 in which the measured voltagesensed by the first voltage sensing plate is V_(top), the measuredvoltage sensed by the second voltage sensing plate is V_(bottom), andthe weighted average calculation is V_(avg)=(1−c)V_(top)+c V_(bot) wherec is a constant weighting factor.
 17. The method of claim 14 furtherincluding measuring power line current and measuring power and energyusing a current measurement and a measured voltage sensed only by thesecond voltage sensing plate.
 18. The method of claim 17 furtherincluding applying a scaling factor to said power and energymeasurements.
 19. The method of claim 18 in which said scaling factor isa function of the measured voltage sensed by the first voltage sensingplate and the measured voltage sensed by the second voltage sensingplate.
 20. The method of claim 19 in which the measured voltage sensedby the first voltage sensing plate is V_(top), the measured voltagesensing by the second voltage sensing plate is V_(bot), and the scalingfactor is (1−c)V_(top)+c V_(bot) divided by V_(bot) where c is aconstant weighting factor.
 21. The method of claim 14 in whichmitigating variations in said measurements includes comparing themeasured voltage sensed by the first voltage sensing plate and themeasured voltage sensed by the second voltage sensing plate.
 22. Themethod of claim 21 further including reporting a snow event when themeasured voltage sensed by the first voltage sensing plate differs fromthe measured voltage sensed by the second voltage sensing plate by apredetermined value.
 23. The method of claim 14 in which there are twoelectrically connected voltage sensing plates exposed to rain and snowand two electrically connected voltage sensing plates shield from rainand snow.
 24. An ungrounded power line sensor system comprising: ahousing configured for disposal about a power line; a current sensorassociated with the housing for measuring power line current; a firstvoltage sensing plate supported by the housing and exposed to rain andsnow; a second voltage sensing plate supported by the housing andshielded from rain and snow; and a processing subsystem configured to:measure a voltage sensed by the first voltage sensing plate, measure avoltage sensed by the second voltage sensing plate, mitigate variationsin said measurements by applying a weighted average calculation to saidvoltage measurements to cancel out the effects of rain on the firstvoltage sensing plate, and measure power and energy using the power linecurrent measurement and only the measured voltage sensed by the secondvoltage sensing plate.
 25. An ungrounded power line sensing methodcomprising: measuring a voltage sensed by a first voltage sensing plateproximate a power line and exposed to rain and snow; measuring a voltagesensed by a second voltage sensing plate proximate a power line andshielded from rain and snow; measuring power line current; applying aweighted average calculation to said voltage measurements to cancel outthe effects of rain on the first voltage sensing plate; and measuringpower and energy using the measured current and only the measuredvoltage sensed by the second voltage sensing plate.